1. Field of the Invention
The present invention relates to optical recognition systems and methods thereof, and, more particularly, to an optical recognition system and a method that adopts a single-slope analog-to-digital converter to proceed a single-slope analog-to-digital conversion in order to have an image with a wide dynamic range.
2. Description of the Prior Art
Please refer to FIG. 6, which illustrates a schematic pixel view of a highly-illuminated area of Taiwanese patent no. I350104, entitled “METHOD, APPARATUS, AND SYSTEM PROVIDING AN IMAGER WITH PIXELS HAVING EXTENDED DYNAMIC RANGE.” As shown in FIG. 6, the dynamic range of a pixel is increased by using selective photosensor resets during a frame time of image capture at a timing depending on the light intensity that the pixel will be exposed to during the frame time. Pixels that will be exposed to high light intensity are reset later in the frame than pixels that will be exposed to lower intensity. The method includes the steps of: determining a pixel value that will be exposed in a light intensity during a frame time; using a timing depending on the determined on the light intensity to reset accumulated charges in a photosensor of the pixel during the frame time; transferring the charges in the photosensor to a store area; and generating a pixel image signal based on the charges transferred to the store area.
In another word, the illumination value of every pixel is stored in a memory. Then the pixels with the same illuminations are divided into plural pixel areas, and the dimensions of each pixel area are stored in the memory. As shown in FIG. 6, there are four image fields of illumination areas 1′, 2′, 3′, and 4′, and therefore four corresponding pixel sets are generated. Thus, any of the four illumination areas 1′, 2′, 3′, and 4′ is constructed by the pixel with the same illumination.
However, aforesaid prior art discloses that of using the timing depending on the pixel exposed in the light intensity during the frame time to reset the photosensor, presenting the four illumination areas for sensing, and the information of each illumination area being stored in the register (memory). Since the additional memory is a must for storing information, the cost of hardware is increased.
Please refer to FIG. 7, which illustrates a schematic system of U.S. Pat. No. 6,707,410, entitled “DIGITAL PIXEL SENSOR WITH A DYNAMIC COMPARATOR HAVING REDUCED THRESHOLD VOLTAGE SENSITIVITY.” The digital pixel sensor architecture 200 has a frame memory 210, and incorporates a new comparator and divides the analog-to-digital conversion circuitry between each pixel and a column processing circuit of the pixel array. The digital conversions are performed one row at a time, instead of for the entire array at once. The row-by-row digitization does not degrade the speed of the DPS architecture since the speed of an imaging system is typically limited by a chip's off-chip data output rate. The row-by-row digitization is also advantageous. The digitized values are stored in the separate frame memory 210 independent of the pixel circuitry. Hence, the frame memory 210 is a must for storing information as well, and the prior art, U.S. Pat. No. 6,707,410, is still added with the cost of hardware.
Thus, how to design an optical recognition system and a method thereof for effectively accessing information, being without additional memory to speed up access, degrading consumption of power, and the dimensions of a chip shall be an important issue for the skilled people.